Tracing the Plastic Tide: Assessing Microplastic Abundance and Distribution along the Attanagalu River in Sri Lanka

Abstract Microplastics (MPs) are a matter of concern as persistent, ubiquitous pollutants that pose a significant threat to biota. MP research has focused on the marine and coastal environment, despite the susceptibility of freshwater bodies to MP pollution due to their frequent interaction with pollution sources. Assessing the abundance and distribution of MPs in freshwater bodies and identifying their origin are required to assess their adverse impact on biota. Here, surface water and sediment samples were collected from 15 strategically selected sites along the Attanagalu River stretch. MPs were recorded in all water and sediment samples. MP abundance ranged from 1.12 to 17.45 items m⁻³ in surface water and 11.38–129.47 items kg⁻¹ in sediment. The highest MP concentrations were recorded near the river mouth, a densely populated, complex hydrodynamic environment. The lowest MP concentration was recorded at the river's head, where a low population density was observed. Secondary MPs were only detected, and fiber was the dominant category in both surface water and sediment samples. Raman Spectroscopy indicated the presence of MPs of polypropylene, polyethylene, polystyrene, and polyvinyl chloride polymers in the river. This finding reveals the prevalence of MPs in the Attanagalu River, and their abundance varies along the river because of the influence of anthropogenic and hydrogeological factors. Further studies are required to identify pollution sources, potential accumulation zones, and quantify the MPs load transported via the river to the Negombo estuarine lagoon.